The correct answer is Option A: Sclereids. Here's why:

Sclereids are a type of sclerenchyma tissue, characterized by their thick, lignified cell walls. These rigid cells provide structural support and protection. They are commonly found in the hard, protective layers of nuts and the gritty texture of pear pulp. Let's break down why the other options are incorrect:

• Fibres are another type of sclerenchyma tissue, but they are long and slender, providing tensile strength. While they are present in some plant structures, they are not the primary component of nut shells or pear pulp.
• Parenchyma cells are thin-walled and loosely packed, making them suitable for storage and photosynthesis. They are found throughout plants but don't provide the same level of rigidity as sclereids.
• Collenchyma cells have thickened cell walls at the corners, offering flexibility and support to young, growing tissues. They are not typically found in mature fruit structures.

In summary, the presence of sclereids with their thick, lignified walls explains the hardness of nut shells and the gritty texture of pear pulp.